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1.
The thermal shock fatigue behaviors of pure hot-pressed alumina and 30 wt. % TiC/Al2O3 composites were studied. The effect of TiC and Al2O3 starting particle size on the mechanical properties of the composites was discussed. Indentation-quench test was conducted to evaluate the effect of thermal fatigue temperature difference (ΔT) and number of thermal cycles (N) on fatigue crack growth (Δα). The mechanical properties and thermal fatigue resistance of TiC/Al2O3 composites are remarkably improved by the addition of TiC. The thermal shock fatigue of monolithic alumina and TiC/Al2O3 composites is due to a "true" cycling effect (thermal fatigue). Crack deflection and bridging are the predominant reasons for the improvement of thermal shock fatigue resistance of the composites. 相似文献
2.
Rui-xia Shi Jia Li Dong-zhi Wang Yan-sheng Yin 《Journal of Materials Engineering and Performance》2009,18(4):414-419
Ductile cobalt was introduced into Al2O3-TiC (AT) composites by using a chemical deposition method to improve toughness and resistance to thermal shock. The mixture
of Co-coated Al2O3 and TiC powders was hot-pressed into an Al2O3-TiC-Co (ATC) composite. The flexure strength and fracture toughness of the ATC composites have been improved considerably,
compared with AT and Al2O3. The fracture surface of ATC shows a large proportion of transgranular cracks with some intergranular type, unlike the intergranular
fracture modes of AT and Al2O3. The thermal shock properties of the composites were evaluated by water quenching technique and compared with the traditional
AT and Al2O3. The composites containing only 3.96 vol.% cobalt exhibited higher critical temperature difference and retained flexure strength.
The SEM examination of the fracture surfaces of the ATC composites after single thermal cycle showed that voids increased
in number and size, and most isolated voids coalesced with increasing temperature difference, which caused the density and
strength to decrease. The ATC composite is less sensitive to repeated thermal shock than the AT composite. 相似文献
3.
S.A. Sajjadi M. Torabi PariziH.R. Ezatpour A. Sedghi 《Journal of Alloys and Compounds》2012,511(1):226-231
Aluminum/alumina composites are used in automotive and aerospace industries due to their low density and good mechanical strength. In this study, compocasting was used to fabricate aluminum-matrix composite reinforced with micro and nano-alumina particles. Different weight fractions of micro (3, 5 and 7.5 wt.%) and nano (1, 2, 3 and 4 wt.%) alumina particles were injected by argon gas into the semi-solid state A356 aluminum alloy and stirred by a mechanical stirrer with different speeds of 200, 300 and 450 rpm. The microstructure of the composite samples was investigated by Optical and Scanning Electron Microscopy. Also, density and hardness variation of micro and nano composites were measured. The microstructure study results revealed that application of compocasting process led to a transformation of a dendritic to a nondendritic structure of the matrix alloy. The SEM micrographs revealed that Al2O3 nano particles were surrounded by silicon eutectic and inclined to move toward inter-dendritic regions. They were dispersed uniformly in the matrix when 1, 2 and 3 wt.% nano Al2O3 or 3 and 5 wt.% micro Al2O3 was added, while, further increase in Al2O3 (4 wt.% nano Al2O3 and 7.5 wt.% micro Al2O3) led to agglomeration. The density measurements showed that the amount of porosity in the composites increased with increasing weight fraction and speed of stirring and decreasing particle size. The hardness results indicated that the hardness of the composites increased with decreasing size and increasing weight fraction of particles. 相似文献
4.
采用固-液相共混法制备了多种BN/Al2O3复合粉末,通过冻融法和表面修饰法对BN进行了改性处理,改变表面修饰剂类型和摩尔比得到了前驱体和烧结态BN/Al2O3复合粉末,并利用机械混合法制备了聚合物基BN/Al2O3复合材料,并测试分析了其导热性能。结果表明,经冻融处理的BN分散性和界面相容性明显优于未经冻融处理的BN。多巴胺对BN的改性效果优于聚乙二醇。采用多巴胺作为表面修饰剂且BN与Al(NO3)3的摩尔比为1:1时,能够得到纳米Al2O3均匀包覆的微米BN粉末,即BN/Al2O3微纳复合粉末,其聚合物基复合材料的导热系数可达0.62 W·m-1·K-1,是纯聚合物导热系数的3倍,是采用纯微米BN粉末制备的聚合物基复合材料导热系数的1.5倍。在BN表面附着的Al2O3可以形成层状热传导通道,能够有效提高聚合物基BN/Al2O3复合材料的热导率。 相似文献
5.
Y3Al5O12 and ZrO2-Y2O3 (8 mol% YSZ) coatings for potential application as thermal barrier coatings were prepared by combustion spray pyrolysis. Thermal cycling of as deposited coatings on stainless steel and FeCrAlY bond coat substrates was carried out at 1000 °C and 1200 °C to determine the thermal fatigue response. Structural and morphological studies on Y3Al5O12 and 8 mol% YSZ coatings before and after thermal cycling have been carried out. It has been noted that the coatings on FeCrAlY substrates remain intact after 50 cycles between room temperature and 1200 °C, whereas the coatings on stainless steel show some minor damage such as peeling off near the periphery after 50 cycles at 1000 °C. Thermal diffusivity values of Y3Al5O12 and 8 mol% YSZ films were measured by using photo thermal deflection spectroscopy and the values are lower than those of coatings produced by conventional techniques such as EBPVD and APS. 相似文献
6.
Chia-Che Chuang Hsing-I Hsiang Jenn Shyong Hwang Tai Shen Wang 《Journal of Alloys and Compounds》2009,470(1-2):387-392
Al2O3-Ce0.5Zr0.5O2 catalytic powders were synthesized by the coprecipitation (ACZ-C) and mechanical mixing (ACZ-M) methods, respectively. As-synthesized powders were characterized by XRD, Raman spectroscopy, surface area and thermogravimetric analyses. It was found that the mixing extent of Al3+ ions affected the phase development, texture and oxygen storage capacity (OSC) of the Ce0.5Zr0.5O2 powder. Single phase of ACZ-C could be maintained without phase separation and inhibit α-Al2O3 formation up to 1200 °C. The specific surface area value of ACZ-C (81.5 m2/g) was larger than that of ACZ-M (62.1 m2/g) and Ce0.5Zr0.5O2 (17.1 m2/g) powders, which were calcined at 1000 °C. In comparison with ACZ-C and Al2O3, which were calcined at high temperature (900–1200 °C), it was found that the degradation rate of specific surface area of ACZ-C was lower than that of Al2O3. ACZ-C sample showed a higher thermal stability to resist phase separation and crystallite growth, which enhanced the oxygen storage capacity property for Ce0.5Zr0.5O2 powders. 相似文献
7.
为了提高热障涂层(TBC)的抗沉积物(主要成分为CaO、MgO、Al2O3和SiO2,简称CMAS)腐蚀性能,采用磁过滤阴极真空电弧(FCVA)技术在TBC表面上制备了致密的Al2O3覆盖层,比较和分析了Al2O3改性TBC和沉积态TBC的润湿行为和抗CMAS腐蚀性能。结果表明:使用FCVA技术制备Al2O3覆盖层的过程对7%(质量分数)氧化钇稳定的氧化锆(7YSZ)相的结构无明显影响,且经Al2O3改性的TBC综合性能均优于沉积态TBC。在1250 ℃、CMAS腐蚀条件下,Al2O3覆盖层有效地限制了熔融CMAS在TBC表面上的扩散行为。同时,Al2O3填充了7YSZ柱状晶之间的间隔并且阻碍了熔融CMAS的渗透,证明了FCVA可作为一种制备Al2O3涂层的新方法以提高TBC的抗CMAS腐蚀性能,且Al2O3涂层及其制备过程对TBC的热震性能均无消极影响。 相似文献
8.
In this paper, ultrasonic surface finishing has been introduced to the electro-discharge machined (EDMed) Al2O3/TiC/Mo/Ni ceramic composite. Thermal shock behavior of the EDMed and the modified ceramic specimens was investigated by water quench tests. Statistical analysis was used to evaluate the thermal shock behavior by measuring the retained strength and determining the strength distributions. Results show that under no thermal shocking conditions, ultrasonic surface finishing for the EDMed ceramic specimens can yield an apparent strengthening with a concurrent increase in Weibull modulus. During rapid quenching, the retained strength and the Weibull modulus of the EDMed specimens can be greatly improved by ultrasonic surface finishing until the temperature difference reaches its critical value (ΔTc). 相似文献
9.
Rui-xia Shi Jianrong Wang Jia Li Yan-sheng Yin 《International Journal of Refractory Metals and Hard Materials》2011,29(6):692-697
The oxidation behavior of hot-pressed Al2O3–TiC–Co composites prepared from cobalt-coated powders has been studied in air in the temperature range from 200 °C to 1000 °C for 25 h. The oxidation resistance of Al2O3–TiC–Co composites increases with the increase of sintering temperature at 800 °C and 1000 °C. The oxidation surfaces were studied by XRD and SEM. The oxidation kinetics of Al2O3–TiC–Co composites follows a rate that is faster than the parabolic-rate law at 800 °C and 1000 °C. The mechanism of oxidation has been analyzed using thermodynamic and kinetic considerations. 相似文献
10.
采用搅拌摩擦加工方法在Al基体中添加不同La2O3含量的混合粉末(Ni+La2O3),制备 (Ni+La2O3)/Al复合材料。采用SEM、EDS、 EPMA及XRD对复合区微观结构及相组成进行分析,采用室温拉伸试验对 (Ni+La2O3)/Al复合材料力学性能进行了测试。结果表明,随着La2O3含量的增加,(Ni+La2O3)/Al复合材料的组织和性能先变好后变差。当La2O3添加量达到5%时,复合材料中Al3Ni增强颗粒分布均匀、颗粒数量最多,块状的Ni粉团聚减少,其抗拉强度达到最大值215MPa,相比Ni/Al复合材料(抗拉强度176MPa),其抗拉强度提高了22%;当La2O3的添加量为7%时,复合材料中Al3Ni增强颗粒含量减少,块状Ni粉团聚重新出现,抗拉强度下降至201MPa。 相似文献
11.
The starting materials of Al2O3, TiO2, ZrO2 and CeO2 nanoparticles were agglomerated into sprayable feedstock powders and plasma sprayed to form nanostructured coatings. There were net structures and fused structures in plasma sprayed nanostructured Al2O3–13 wt.%TiO2 coatings. The net structures were derived from partially melted feedstock powders and the fused structures were derived from fully melted feedstock powders. The nanostructured Al2O3–13 wt.%TiO2 coatings possessed higher hardness, bonding strength and crack growth resistance than conventional Metco 130 coatings which were mainly composed of lamellar fused structures. The higher toughness and strength of nanostructured Al2O3–13 wt.%TiO2 coatings were mainly related to the obtained net structures. 相似文献
12.
The thermal shock behavior of three kinds of Al2O3/13 wt%TiO2 coatings fabricated by plasma spraying was studied in this paper. One kind of those coatings was derived from conventional fused and crushed feedstock powder available commercially; the other two kinds of coatings were derived from nanostructured agglomerated feedstock powders. These two nano coatings possess moderate pores and pre-existing microcracks, they were composed of fused structure and three-dimensional net or skeleton-like structure. For conventional coatings, the pores and pre-existing cracks were bigger, sharp-point and mostly distributed between splats. Thermal shock tests for the three coatings were performed by water quenching method. Testing result showed the two kinds of nano coatings had much higher thermal shock resistance than the conventional coatings. The improved thermal shock resistance for nano coatings could attribute to their improved microstructure and crack propagation mode. The damage evolution and failure mechanism of coatings was quite different at thermal shock temperature of 650 °C and 850 °C, which was explained by a simple model. Different crack propagating modes in nanostructured and conventional coatings during thermal shock tests were due to their different microstructures in these two kinds coatings. The stress state of coating surfaces during the thermal cycles was also discussed in this paper. 相似文献
13.
微弧氧化技术是一门新的表面处理技术,在很多领域有着广泛的应用前景,但其结构受限于电解液成分。本文通过在磷酸盐电解液中加入Al2O3陶瓷颗粒,使得在Ti6Al4V钛合金表面的微弧氧化涂层结构和性能得到改性。涂层的结构和性能通过扫描电镜和XRD衍射仪进行表征和测试,涂层的抗高温氧化性能和热震性能通过高温热循环氧化试验和热震试验进行测试。结果表明,通过在电解液中添加Al2O3陶瓷颗粒,涂层由Al2TiO5 and TiO2组成,涂层更为致密,表现出更为优异的抗高温氧化和热震性能。电解液中游动的Al2O3陶瓷颗粒在微弧氧化过程中被吸入到样品表面并进入涂层,涂层的结构和性能得到改性。 相似文献
14.
Nano-sized Al2O3 ceramic particles (50 nm) were co-deposited with nickel using electrodeposition technique to develop composite coatings. The coatings were produced in an aqueous nickel bath at different current densities and the research investigated the effect of applied current on microstructure and thickness of the coatings. The variation in some mechanical properties such as hardness, wear resistance, and the adhesive strength of the composite coatings is influenced by the applied current and this was also studied. The morphology of the coatings was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The hardness, wear resistance, and bond strength of the coatings were evaluated by Vickers micro-hardness test, pin-on-disc test, and tensile test, respectively. Results showed that the Al2O3 particles were uniformly distributed in the coatings, and the coatings deposited at a current density of 0.01 A/cm2 was most favorable in achieving a maximum current efficiency which causes the co-deposition of a maximum amount of Al2O3 particles (4.3 wt.%) in the coatings. The increase in Al2O3 particles in the coatings increased the mechanical properties of the Ni-Al2O3 composite coatings by grain refining and dispersion strengthening mechanisms. 相似文献
15.
Yibin Li Yue Sun Wenzhu Zhang Yujie Ding Xiaodong He 《Journal of Alloys and Compounds》2008,460(1-2):115-119
Nanocrystalline aluminum embedded in amorphous dielectric alumina matrix thin films (nc-Al/α-Al2O3) was synthesized via reactive magnetron sputtering. The nc-Al/α-Al2O3 films at different oxygen partial pressures were sputtered on p-type Si substrates from a pure Al target in the mixed ambient of Ar and O2. Both deposition rate and aluminum concentration increase as the oxygen partial pressure decreases. X-ray photoelectron spectroscopy and high-resolution transmission electron microscope studies give the confirmation of nanocrystalline Al embedded in amorphous Al2O3 matrix. This nanocomposite thin film exhibits memory effect as a result of charge trapping. The flat band voltage value depends on the Al nanocrystal concentration which is related to oxygen partial pressure. 相似文献
16.
R.V. Vovk M.A. Obolenskii A.V. Bondarenko I.L. Goulatis A.V. Samoilov A. Chroneos V.M. Pinto Simoes 《Journal of Alloys and Compounds》2008,464(1-2):58-66
The temperature dependence of the transport anisotropy of ReBa2Cu3O7−δ (Re = Y, Ho) single crystals is investigated. We experimentally determine the parallel and perpendicular conductivity in oxygen deficient single crystals. It is found that, in these single crystals, oxygen deficiency results to uneven oxygen distribution within their volume that leads to the formation of superconducting phases with different critical temperatures. We present an analysis regarding the agreement of the experimental data with the predictions of different theoretical models. It is determined that, the absolute values of the energy gaps along and perpendicular to the basis plane are changed, with different signs of their derivatives. When the value of Δc increases, the value of the pseudo-gap decreases and vice versa, testifying that the PG regime is suppressed, with a synchronous strengthening of the localization effects. In distinction to YBa2Cu3O7−δ, the temperature dependence of the anisotropy of the resistivity ρc/ρab(T) for the HoBa2Cu3O7−δ samples is well described, by the universal “law of 1/2” for the thermally activated hopping conductivity. 相似文献
17.
Fancheng MengCheng Liu Fan ZhangZhongqing Tian Weijiu Huang 《Journal of Alloys and Compounds》2012,512(1):63-67
Alumina matrix composites containing 5 and 10 wt% of ZrO2 were sintered under 100 MPa pressure by spark plasma sintering process. Alumina powder with an average particle size of 600 nm and yttria-stabilized zirconia with 16 at% of Y2O3 and with a particle size of 40 nm were used as starting materials. The influence of ZrO2 content and sintering temperature on microstructures and mechanical properties of the composites were investigated. All samples could be fully densified at a temperature lower than 1400 °C. The microstructure analysis indicated that the alumina grains had no significant growth (alumina size controlled in submicron level 0.66-0.79 μm), indicating that the zirconia particles provided a hindering effect on the grain growth of alumina. Vickers hardness and fracture toughness of composites increased with increasing ZrO2 content, and the samples containing 10 wt% of ZrO2 had the highest Vickers hardness of 18 GPa (5 kg load) and fracture toughness of 5.1 MPa m1/2. 相似文献
18.
Surface integrity and material removal mechanisms associated with the EDM of Al2O3 ceramic composite
K.M. Patel Pulak M. Pandey P. Venkateswara Rao 《International Journal of Refractory Metals and Hard Materials》2009,27(5):892-899
Electric discharge machining (EDM) has been proven as an alternate process for machining complex and intricate shapes from the conductive ceramic composites. The performance and reliability of electrical discharge machined ceramic composite components are influenced by strength degradation due to EDM-induced damage. The success of electric discharge machined components in real applications relies on the understanding of material removal mechanisms and the relationship between the EDM parameters and formation of surface and subsurface damages. This paper presents a detailed investigation of machining characteristics, surface integrity and material removal mechanisms of advanced ceramic composite Al2O3–SiCw–TiC with EDM. The surface and subsurface damages have also been assessed and characterized using scanning electron microscopy (SEM). The results provide valuable insight into the dependence of damage and the mechanisms of material removal on EDM conditions. 相似文献
19.
Bulk WC-Al2O3 composites prepared by spark plasma sintering 总被引:1,自引:0,他引:1
Donghai ZhengXiaoqiang Li Xuan AiChao Yang Yuanyuan Li 《International Journal of Refractory Metals and Hard Materials》2012,30(1):51-56
WC and WC-Al2O3 materials without metallic binder addition were densified by spark plasma sintering in the range of 1800-1900 °C. The densification behavior, phase constitution, microstructure and mechanical properties of pure WC and WC-Al2O3 composite were investigated. The addition of Al2O3 facilitates sintering and increases the fracture toughness of the composites to a certain extent. An interesting phenomenon is found that a proper content of Al2O3 additive helps to limit the formation of W2C phase in sintered WC materials. The pure WC specimen possesses a hardness (HV10) of 25.71 GPa, fracture toughness of 4.54 MPa·m1/2, and transverse fracture strength of 862 MPa, while those of WC-6.8 vol.% Al2O3 composites are 24.48 GPa, 6.01 MPa·m1/2, and 1245 MPa respectively. The higher fracture toughness and transverse fracture strength of WC-6.8 vol.% Al2O3 are thought to result from the reduction of W2C phase, the crack-bridging by Al2O3 particles and the local change in fracture mode from intergranular to transgranular. 相似文献
20.
Preparation of the ternary carbide Ti2AlC was conducted by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS) from the elemental powder compacts of Ti:Al:C = 2:1:1, TiC-containing samples with TiC of 6.67–14.3 mol%, and Al4C3-containing samples with Al4C3 of 1.96–10 mol%. Effects of TiC and Al4C3 addition were studied on combustion characteristics and the degree of phase conversion. Due to the growth of laminated Ti2AlC grains, the reactant compact was subjected to an axial elongation during the SHS process. Because the addition of TiC and Al4C3 led to a decrease in the reaction temperature, the flame-front propagation velocity was correspondingly reduced for the TiC- and Al4C3-containing samples when compared with the elemental reactants. Based upon the XRD analysis, formation of Ti2AlC along with a secondary phase TiC was identified in the synthesized products. The grains of Ti2AlC are typically plate-like with a size of 10–20 μm and several laminated Ti2AlC grains form a layered structure. The content of Ti2AlC yielded from the elemental powder compacts is about 85 wt%. The addition of TiC was found to facilitate the formation mechanism and therefore to enhance the extent of Ti2AlC conversion approaching 90 wt%. As a result of the reduced exothermicity of the reaction, however, the content of Ti2AlC decreased slightly in the products synthesized from the Al4C3-added samples. 相似文献